How much fresh air?

G

Greenfing

New Member
I got my 4x4 grow tent set up inside a dedicated room.
My 552m3/h extract fan pulls air from the reflector and out into the room where I got my heater, AC, humidifier and a dehumidifier set up. Right now my source of fresh air is two open windows but that wont work in the winter when temperatures drop below 0c, im looking to buy a air handling unit with heat recovery unit but I dont know how big it should be.

is there any rule of tumb for how much fresh air is needed pr square fot/m2 of growspace?
 
Is there any reason you cant put a thermostat on it?
You can build one, or buy one. They are available on Amazon, home depot.. etc.
The purpose of air exchange is controlling humidity and temperature. But if the humidity and temperature is within the desired range, you can turn off the air exchange for that period of time. until it goes back out of that range.
 
I was thinking about the Co2, how much fresh outside air do I need to bring in pr. hour to keep my plants happy, sorry for not making that clear. The temperatures here can drop to -20C, all intake air to the lung room needs to be preheated and that will start to cost me.
 
My tent all ready got a 552m3/h extraction fan, im asking the size of the intake fan to my lung room from the outside.

My setup;
Growroom2.png
 
Greenfing said:
My tent all ready got a 552m3/h extraction fan, im asking the size of the intake fan to my lung room from the outside.

My setup;
Growroom2.png
Click to expand...
Hello green. I live just 100 miles from the arctic circle, and if it's just as cold where you are, I recommend using the exhaust from your HID light to help heat your house. As long as there is decent circulation in your home, I wouldn't suspect you wouldn't need to bring in tons of icy fresh air. Maybe just a crack on opposing windows to promote a very small amount of cross ventilation, as too much may cost even more to heat and counteract the benefit of fresh air. A submergable water heater for an aquarium in a 5 gallon bucket is a great way to keep temps from dropping too low when your light is off. Hope this helped some. Best of luck.

-dabber
 
Thanks for your answer, but my lung room is inside an insulated room in my garage and there is no ventilation and the room itself is pretty airtight when i close all doors/windows. I had open windows during spring/summer but I need to close the windows for winter or I will/can have weeks where the temps will drop to below 0C even with lights running. I can get a couple of weeks with -25c / -13 degrees Fahrenheit.

So, a crack opened window will cost me approx 10-15Kw/h pr. day during the coldest days. (I tried keeping my chili plants there last winter) and I will have no control over the airflow or If the fresh air actually makes it to my plants or if If it gets heated and sent out the window again.

I need to either set up a small ventilation with a heat exchanger, or I need to install a tiny computerfan intake, but I want to know if there is any m3/m2 requirements. (im sure the indoor plantation guys got some formula)
 
There are rules of thumb that you need X amount of cfm per cubic foot for typical conditions. But the answer is, you need the right amount of airflow to control your temperature and humidity. If your tent is too hot, you need more airflow, if your tent is too cold, you need less airflow. If you get your temperature correct, your humidity should follow. If not, you may need to suppliment with humidifiers/dehumidifiers.
 
Shoot yeah that's like a conundrum a tent in a box in a box.... I chose to avoid the garage for the lack of circulation. The bathroom offers the same problem for me but at least there's the vent, where I will try to have some air sucked out/pushed out. I'm gonna try to use the tub space to flower. So similar. A tent in a box in the center of the house....
That being said my goal is to exchange the air in the bathroom every 90 seconds to 2 minutes. So If give you the same advice. Which ever is the room you said is air tight aim to refresh that "entire" area every 2 mins, max. I'd aim to use active exhaust and passive intake, warming the air as it enters. Did you post size specs?
 
But I also agree with Marc. I'd get your CFM equal to your tent size, So that the air is exchanged every minute. And aim to refresh the lung room every 2. If temp is too low back off and to high the opposite. Hope that helps?
 
Isnt the CFM formula (LxHxW /3=CFM) more as a requirement for removing the heat followed by humidity and general air cirulation?

- Heat is not a problem, I got an AC for sunny days and I need to add heaters for winter.
- Humidity is not a problem, I got a large dehumidifier and cold winter air is about 20%. (I got an humidifier also)
- Changing out all the air in the lung room every 2nd minute (approx. 25m2 x 2,4meter ceiling), by preheating -25C air to 20C will cost me a godzillion dollars (I will need to spend about 250kwh pr day in heating during light period pr day, if my math is correct, 40USD/day in extra heating)

If normal outside air got 400PPM CO2, I want close to that number inside my lungroom, my realistic options are a small computer fan (5-20m2/hour) or a heat exchanger 50-100m3/hour then run the intake in on the floor somewhere close to my tent intake and the extract opposite side close to the ceiling.

How much energy does it take to raise the temperature of an average room by 10 degrees? - Quora
 
Wow didn't expect that size lung room. Let me run some numbers. Hold please :)
 
To calculate cubic feet it is simply l x h x w. That number is the cube footage of the area. Example: 5 foot wide room by 10 foot wide by 10 foot high = 500 cubic feet. If this is the size of your grow area, aim to replace the entire space every minute. Again less or more based on temp and rh.

Ok. I've been struggling with this myself and I think I have your answer! Finally! Sorry I had to look back at the size of your tent. My answer was wrong very wrong b.c you have such a large lung room! Assuming your dimensions in the drawing are in feet, 2x2x4 is 16 cubic feet. If it is metric, approximately 3 feet to a meter, gives us 6x6x12 or 435 cubic feet. The answer is less complicated than I had originally thought. You should aim for the same air exchange of your lung room as your grow space.
Be that 16 CFM or 435 CFM respectively.
 
If found some forums discussing the same question as I got but there is no clear answer to find.
Some people talk about changing out the air in the tent every 2nd, 3rd or 5th minute, but it seems like some general talk and not expert answers. The lower the PPM in the lungroom the more extraction from the tent to the lung room you need, makes sense.

With every 5th minute, I need to replace about 50m2/hour, but that seems like (and is) A LOT more circulation than just running the tent in the basement without an active extract out.

Im still convinced there is some formula for this, pr. plant, M2, M3 or KG.
How long does it take a plant to eat up 400PPM from 1m3 of air?
 
A large robust plant will eat up all 400 ppm every minute. Hence the CFM and need to replace the air every minute. But seems like I'm not giving you the answers you want....
420-magazine-mobile2085635067.jpg


Air Circulation & Exhaust Tutorial | Grow Weed Easy

Hopefully this can help some. Again I ran the numbers yesterday, and math hasn't let me down yet. Even if your using low powered cfls ( the c02 consumption is directly related to power of light) and assuming 0 ventilation after 3 minutes all c02 will be used inside the tent. Bigger better lights will bring that down to 1 minute to eat up all avalible c02. The point is it's impossible to know exactly who much air your plant consumes a minute. But it is always always better to have more fresh air than not enough. Lack of airflow will slow your growth and lessen your yield as well as greatly increasing the chance of pests.

Here's how I calculated needed air flow

Imagine a 1 cubic meter growspace in a 9 cubic meter lung room (10 cubic meters total) Assuming the grow space has a air refresh rate of 1 cubic meter a minute, and the plant uses all avalible c02 within that 1 cubic meter every minute, the lung room also needs to re supply that consumed 1 cubic meter of air every minute also. Again the lung room should have an equal refresh rate to the grow space.

Not sure how else to break it down for you. But I'll let others try. Best of luck!

-dabber
 

Similar threads

simondetroit
Fresh Air?
Replies
6
Views
2K
simondetroit
simondetroit
G
Do thermal pumps reversible cycle air conditioner provide fresh air for plants?
Replies
1
Views
794
Greenfing
G
glassONglass
Fresh air circulation and air cooling
Replies
3
Views
2K
greenmonkey
greenmonkey
C
Outdoor air vs. Indoor air for "fresh air"
Replies
2
Views
2K
c526
C
R
Fresh air in winter and room temp questions
Replies
6
Views
5K
Reetafour
R
Back
Top Bottom